The present invention relates to an image transfer printing film roll fabricated by winding on a bobbin a length of an image transfer printing film to be used in heat-sensitive image transfer recording. The present invention relates also to a method of detecting an end of the transfer printing film when the same is being paid out from the bobbin.
There have been devised and demonstrated heat-sensitive image transfer recording devices of the type in which an image transfer printing film is supplied from a transfer film roll. In a known transfer printing film roll, the trailing end of a length of the image transfer film is partially and lightly attached via an adhesive tape to a bobbin which is a core of a transfer printing film roll, as disclosed in Japanese Utility Model Laid-Open Publication (KOKAI) No. 5863/1985 published Jan. 16, 1985.
With this known transfer printing film roll, only one portion in the direction of the width of the trailing end of the transfer film is attached to the bobbin so that it is difficult to apply a tension of uniform distribution over the width to the transfer printing film which is being wound around the bobbin, and consequently there arise the problems that the side edges of the transfer printing film wound around the bobbin are not aligned with each other and that the transfer printing film is wrinkled. When a transfer printing film roll is used in a heat-sensitive image transfer recording device, an "END" mark must be applied to the film in the vicinity of the trailing end thereof in order that a sensor mounted in the transfer recording device can detect this mark when the film is going to be unwound completely. It is therefore required to apply such an "END" mark on each transfer printing film before the film is rolled on the bobbin. Further, in this type of transfer printing film rolls, the film is easily separated from the bobbin when the film has been unwound completely from the bobbin, if no provision is made for stopping the unwinding operation, since the adhesion of the film to the bobbin is not strong enough.
The above Utility Model Laid-Open Publication No. 5863/1985 also discloses a transfer printing film roll wherein the trailing end of the film has preliminarily applied thereto an adhesive layer in the shape of a strip extending along the trailing edge of the film, the adhesive layer being covered by a release tape. When the trailing end of the transfer printing film is to be attached to the bobbin, the release tape must be removed and then the film is attached to the bobbin. It is inconvenient and troublesome to remove the release tape before attaching the film to the bobbin, and, moreover, the adhesion of the film to the bobbin is not strong enough again.